walid Posted May 19, 2006 Report Share Posted May 19, 2006 (1) I read carefully the CM8870 datasheets but I can't conclude that it can receive the FM signal directly or it must be connected to a separated FM receiver please tell me(2) I hardly got the datasheets of CM8870/70C, but i really have CM8870PI Is there any difference?thanx Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 19, 2006 Report Share Posted May 19, 2006 Hi Walid,It is just a DTMF tones decoder. It has nothing to do with a radio.Get a good datasheet from www.datasheetarchive.com .If you use an ordinary FM broadcast band radio then it has de-emphasis and the transmitter that you use must have a matching pre-emphasis. Quote Link to comment Share on other sites More sharing options...
walid Posted May 20, 2006 Author Report Share Posted May 20, 2006 It is just a DTMF tones decoder. It has nothing to do with a radio.i understand that it require a separate FM receiverGet a good datasheet from www.datasheetarchive.com .i use this link but i have not any resultsbut in this http://www.alldatasheet.com/ i faound manyIf you use an ordinary FM broadcast band radio then it has de-emphasis and the transmitter that you use must have a matching pre-emphasis.i'm not understand this statementthank you Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 20, 2006 Report Share Posted May 20, 2006 Hi Walid,To reduce hiss, FM stations and TV stations use pre-emphasis for their audio transmission, and FM receivers have a corresponding de-emphasis.Pre-emphasis boosts high audio frequencies and the de-emphasis cuts them back to normal and also cuts hiss.DTMF needs a frequency response that is fairly flat, but if you don't use pre-emphasis in its transmission then a receiver's de-emphasis will cut high tones frequencies too much. Quote Link to comment Share on other sites More sharing options...
walid Posted May 21, 2006 Author Report Share Posted May 21, 2006 OK Mr audioguruI may understand the general aspect of what u said butcan u give me an example about this especially on your FM transmitter circuit.where the subcircuit or the parts that do the pre-emphasis also in the receiver where it be placed in the whole circuitthank u audioguru Quote Link to comment Share on other sites More sharing options...
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